Ul small nuclear RNAs (Ul RNAs) are abundant RNA molecules which, in the form of Ul-ribonucleoprotein particles (Ul snRNPs) are found in the nuclei of all higher eukaryotes; they are generally thought to be essential for the process of pre-mRNA splicing. The long-range goals of this project are to define the structures required for Ul RNA synthesis and function, and to elucidate how differential accumulation of Ul RNAs influences overall gene expression. The work will be carried out in three different organisms, human, frog and mouse, in order to utilize particular advantages of each system. The structural features of Ul DNA templates and Ul RNAs will be probed by introduction of wild-type or mutated Ul RNA genes into transcription systems either by microinjection or by transfection. Sequences upstream, downstream, and within the coding regions of cloned human and X. laevis Ul RNA genes will be analyzed for their function in transcription and roles in formation of mature Ul snRNPs. The newly synthesized Ul RNAs and/or Ul snRNPs will be characterized with respect to 5' and 3' maturation, base modification, association with snRNP proteins, and their ability to participate in the splicing of pre-mRNAs. Assays for participation of specific Ul RNAs in pre-mRNA splicing will be developed and applied to the analysis of how Ul RNA functions. The developmental control of Ul RNA gene expression will be studied in both frog and mouse embryos and tissues. The stages at which U1 gene expression changes from the embryonic to the somatic pattern will be determined and the mechanisms of control will be investigated. The ability of the different types of Ul RNAs to support the splicing of a variety of pre-mRNAs will be tested, as well as the ability of these RNAs to bind the normal complement of snRNP-associated proteins.